Field of the Disclosure
The present application relates to a fiber-optic-based laser that generates light between about 189 nm and about 200 nm in wavelength, such as light at a wavelength near 193 nm, and is suitable for use in photomask, reticle, or wafer inspection.
Related Art
The integrated circuit industry requires inspection tools with increasingly higher resolution to resolve ever smaller features of integrated circuits, photomasks, solar cells, charge coupled devices etc., as well as detect defects whose sizes are of the order of, or smaller than, feature sizes. Short wavelength light sources, e.g. sources generating light under 200 nm, can provide such resolution. However, the light sources capable of providing such short wavelength light are substantially limited to excimer lasers and a small number of solid-state and fiber lasers. Unfortunately, each of these lasers has significant disadvantages.
An excimer laser generates an ultraviolet light, which is commonly used in the production of integrated circuits. An excimer laser typically uses a combination of a noble gas and a reactive gas under high pressure conditions to generate the ultraviolet light. A conventional excimer laser generating 193.4 nm wavelength light, which is increasingly a highly desirable wavelength in the integrated circuit industry, uses argon (as the noble gas) and fluorine (as the reactive gas). Unfortunately, fluorine is toxic and corrosive, thereby resulting in high cost of ownership. Moreover, such lasers are not well suited to inspection applications because of their low repetition rate (typically from about 100 Hz to several kHz) and very high peak power that would result in damage of samples during inspection.
A small number of solid-state and fiber-based lasers producing sub-200 nm output are known in the art. Unfortunately, most of these lasers have very low power output (e.g. under 60 mW), or very complex design, such as two different fundamental sources or eighth harmonic generation, both of which are complex, unstable, expensive and/or commercially unattractive.
Therefore, a need arises for a laser capable of generating 193 nm light, yet overcoming the above disadvantages.